Help with Orange Terror Bass Repair

My son uses an Orange Terror Bass 500 (which is out of warranty) and at a show tonight, it must have gotten kicked or something hit it because the plastic Gain knob has popped off. He still has the knob but it looks like the Gain shaft is bent and it's floppy in its hole.

I tried to tighten the washer that holds the outer shaft in place but when I do, the inner shaft will no longer rotate like its supposed to and when you do turn it, it loosens up the entire shaft again.

Is this something that can be repaired easily, possibly by myself or is this something that will need an amp tech?